Warn that mapped-drive ranks must stay distinct

Two statuses sharing a rank makes min() break the tie by argument order, so the same drive reads healthy or broken depending on which source enumerated first. Deliberate synonyms are safe because either answer is the same answer; a new status landing on an existing rank is not, and the rank table is where someone adding one will be looking.

Names the test that catches it, since the single-direction tests stay green through this and would otherwise suggest the change was safe.

plugins/endpoints/api/routes.py

@@ -685,6 +685,17 @@ def _drive_letter(value):
 # Worst-first. The panel shows the worse of the two sources for a drive, so a
 # share that one source calls OK and the other calls Unavailable is reported as
 # Unavailable: a drive that is broken in either view is broken for the operator.
+#
+# WARNING - ranks must stay DISTINCT across statuses that can genuinely differ.
+# _worse_drive_status resolves by min(), which breaks a tie by argument order,
+# so two statuses sharing a rank make the verdict depend on which SOURCE
+# happened to report which - the same drive reads healthy or broken based on
+# enumeration order. Deliberate synonyms are fine (disconnected/unavailable,
+# ok/connected) because either answer is the same answer. Adding a NEW status at
+# an existing rank is not. test_which_source_reported_a_status_does_not_change
+# _the_verdict in tests/test_plugins/test_endpoints_mapped_drives.py asserts
+# both directions of each pair and is what catches this; the single-direction
+# tests stay green through it.
 _DRIVE_STATUS_RANK = {
     'unavailable': 0,
     'disconnected': 0,